Semiconductor elements such as, for example, a large scale integrated circuit (LSI), a metal oxide semiconductor (MOS) transistor, a liquid crystal display (LCD), and an electro luminescence (EL) element, are manufactured by performing a processing such as, for example, etching, chemical vapor deposition (CVD), or sputtering, on a processing target substrate which is an object to be processed. The processings such as, for example, etching, CVD and sputtering, include processing methods using plasma as an energy supply source, i.e., plasma etching, plasma CVD, and plasma sputtering.
In a plasma processing apparatus performing a processing using plasma generated by microwaves, a magnetron may be used as a high frequency generating source when generating microwaves. The magnetron is effectively used as a microwave generating source since it may be configured relatively inexpensively. Further, the magnetron may output a high power. Japanese Patent Laid-Open Publication No. 2006-94214 (Patent Document 1), Japanese Patent Laid-Open Publication No. 2007-82172 (Patent Document 2), and Japanese Patent Laid-Open Publication No. 2010-283678 (Patent Document 3) disclose technics related to the magnetron.
According to Patent Document 1, a magnetron oscillation device is provided with a reference signal supply unit and an impedance generator so as to adjust a load impedance of a magnetron. In addition, according to Patent Document 2, a magnetron oscillation device is configured to be provided with an irreversible member. Further, according to Patent Document 3, a shift from a desired oscillation frequency is detected so as to generate a shift signal in a magnetron oscillation device, and a driving voltage having a frequency desired by the oscillation frequency of a magnetron is generated based on the shift signal and output to an impedance generator.